The invention relates to improvements in fluid-operated motors in general, and more particularly to improvements in apparatus which can be utilized in the power trains of motor vehicles to change the condition of engageable-disengageable torque transmitting devices. Still more particularly, the invention relates to improvements in apparatus which can be utilized with advantage to change the condition of friction clutches serving to establish or to interrupt a torque transmitting connection between a prime mover (such as an internal combustion engine) and a transmission or another torque-receiving unit in the power train of a motor vehicle.
In many presently utilized types of motor vehicles, the clutch actuating apparatus comprises a first hydraulic cylinder and piston unit known as slave cylinder and serving to disengage the friction clutch in response to shifting of its piston relative to its cylinder (hereinafter called housing) as a result of admission into the housing of a flow of pressurized hydraulic fluid from a second hydraulic cylinder and piston unit known as master cylinder. Reference may be had, for example, to commonly owned U.S. Pat. No. 5,632,706 granted May 27, 1997 to Kremmling et al. for xe2x80x9cMOTOR VEHICLE WITH ELECTRONIC CLUTCH MANAGEMENT SYSTEMxe2x80x9d. In the patented power train, the piston of the slave cylinder is arranged to pivot a lever serving to shift a release bearing which is arranged to change the conicity of a diaphragm spring forming part of the friction clutch and serving to urge a pressure plate against the friction linings of a clutch disc as long as the clutch is engaged. The diaphragm spring is free to reengage the clutch as soon as the piston of the slave cylinder is free or is caused to return to its retracted position in the housing of the slave cylinder. When the clutch is engaged, it causes or enables the output shaft (such as a crankshaft or a camshaft) of the engine to transmit torque to a change-speed transmission so that the latter can transmit torque to the front and/or rear wheels of the motor vehicle, e.g., by way of a differential.
The slave cylinder is or can be coaxial with the output shaft of the engine, and its housing can be separably mounted on the case of the transmission. The piston of the slave cylinder can constitute an annular member which is slidable in an axial bore or hole of the housing and slidably surrounds a sleeve-like guide which is sealingly and fixedly (such as non-rotatably and/or non-shiftably) affixed to the housing and/or to another stationary part, e.g., to the transmission case. The piston, the housing and the sleeve-like guide (hereinafter called guide for short) define an annular plenum chamber which can receive pressurized hydraulic fuid (such as oil) from the master cylinder. The rear end portion of the piston carries an annular sealing member which is in sealing engagement with but can slide along the internal surface of the housing as well as along the external surface of the guide. The front end portion of the piston carries or indirectly transmits motion to a release bearing which can disengage the friction clutch in response to admission of pressurized hydraulic fluid into the plenum chamber of the slave cylinder. As already mentioned above, the release bearing can be coaxial with the output shaft of the engine and with the diaphragm spring of the clutch, or it can change the conicity of the diaphragm spring by way of a lever (e.g., the so-called clutch fork).
A slave cylinder of the just outlined character is described and shown, for example, in published German patent application Ser. No. 43 13 346 A1. The guide is made in accordance with a non-cutting shaping technique (e.g., in a deep drawing machine) and one of its ends is provided with a flange adjacent the transmission case and form-lockingly connected with the housing of the slave cylinder. The flange can also serve as a boundary for one end of the annular plenum chamber of the slave cylinder. In addition, an axially projecting part of the flange can perform a centering function in that it extends into a complementary recess of the housing.
When the slave cylinder is properly assembled, the annular flange of the guide is clamped between the transmission case and a part of the clutch disengaging unit to thus hold the guide in a predetermined axial position. The means for establishing a seal between the guide and the housing of the slave cylinder comprises an annular seal which is radially offset relative to the annular plenum chamber. When such annular seal is acted upon by pressurized hydraulic fluid, it provides a relatively large effective pressurized surface extending from the external surface of the guide to the seal, i.e., radially of and well beyond the cross-sectional area of the plenum chamber. This causes the housing of the slave cylinder to undergo a pronounced stress. Therefore, the dimensions of the housing must be increased accordingly and/or the quality of the material of the housing must be selected with a view to ensure that the slave cylinder and its parts will be capable of withstanding the developing stresses (particularly deforming stresses), preferably during the entire useful life of the power train.
Other presently known types of slave cylinders for use in the power trains of motor vehicles are disclosed in pubished UK patent application Serial No. 2 259 555 of Grosspletsch et al., in published French patent application Serial No. 2 597 590, and in published European patent application Serial No. 0 168 932. The disclosure of the commonly owned German priority application Serial No. 198 25 965.4 (filed Jun. 10, 1998) as well as that of each U.S. and/or foreign patent and/or patent application identified in the specification of the present application is incorporated herein by reference.
An object of the invention is to provide a slave cylinder wherein the sealing device(s) between the constituents of the slave cylinder is or are simpler, more compact and less expensive than, but at least as reliable as, in presently known slave cylinders.
Another object of the invention is to provide a slave cylinder wherein the seal between the tubular guide and the housing is constructed, assembled and installed in such a way that these parts are not subjected to stresses which would necessitate the utilization of bulkier and/or otherwise more expensive parts.
A further object of the invention is to provide a novel housing and a novel tubular guide for use in the slave cylinder of a clutch disengaging system in the power train of a motor vehicle.
An additional object of the invention is to provide a novel and improved disengaging unit for the friction clutches of power trains in motor vehicles.
Still another object of the invention is to provide a novel and improved method of establishing one or more seals between selected constituents of the clutch actuating apparatus in the power train of a motor vehicle.
A further object of the present invention is to provide a novel and improved arrangement of confining and locating one or more sealing elements between the constituents of a slave cylinder in a clutch engaging-disengaging assembly forming part of the clutch actuating apparatus in the power train of a motor vehicle.
The invention is embodied in a fluid-operated apparatus which can be utilized as a clutch actuating apparatus in the power train of a motor vehicle, for example, in a power train wherein a shaft (such as the output shaft of an engine or another prime mover or the input shaft of a change-speed transmission or another torque-receiving unit) is rotatable about a predetermined axis. The improved actuating apparatus can constitute a slave cylinder which is actuatable to engage and/or disengage a friction clutch and comprises a support (such as the case of a change-speed transmission), a housing or cylinder which is separably or more or less permanently mounted on the support and has a cylindrical internal surface coaxial with and spacedly surrounding the aforementioned shaft, and a tubular guide which surrounds the shaft and has a cylindrical external surface coaxial with and spacedly surrounded by the internal surface of the housing. The housing has a preferably annular centering portion and the guide has an end portion which is centered by the annular portion of the housing. The apparatus further comprises at least one annular sealing element which is interposed between the end portion of the guide and the centering portion of the housing. The internal surface of the housing is located at a first radial distance from the predetermined axis and the radially outermost portion of the at least one sealing element is disposed at a second radial distance from such axis; the second radial distance at most equals but can be less or even considerably less than the first distance. Still further, the improved apparatus comprises an annular piston which is coaxial with and is reciprocable between the internal and external surfaces and defines with such surfaces (i.e., with the guide and the housing) an annular plenum chamber which can receive a pressurized fluid (preferably a hydraulic fluid) from a suitable source, e.g., from a master cylinder in the power train of the motor vehicle.
In accordance with a presently preferred embodiment, the improved apparatus further comprises means (such as mating male and female coupling members) for separably coupling the housing to its support (such as to the aforementioned housing or case of a change-speed transmission).
That end portion of the piston which is remote from the plenum chamber and from the centering portion of the housing can serve to support and to reciprocate a suitable clutch release bearing, e.g., a bearing which can serve to tilt a diaphragm spring relative to the housing of a friction clutch in the power train of a motor vehicle. Reference may be had, for example, to FIG. 2 of commonly owned U.S. Pat. No. 5,409,091 granted Apr. 25, 1995 to Reik et al. for xe2x80x9cAUTOMATICALLY ADJUSTABLE FRICTION CLUTCHxe2x80x9d.
The housing can comprise or support means for maintaining the guide in a predetermined axial position relative to the internal surface and the centering portion of the housing.
The end portion of the guide can include an annular flange which extends substantially radially of and away from the predetermined axis; such end portion of the guide and the adjacent portion of the housing (such as the aforementioned centering portion) can define an annular compartment which is disposed radially outwardly of the annular flange. The compartment can be provided with an open side which confronts the centering portion of the housing, and the end portion of the guide can further include a second annular flange which is located radially outwardly of the annular compartment. At least one of the two annular flanges can be disposed in a plane which is at least substantially normal to the predetermined axis. An end face of the centering portion of the housing can confront the open side of the annular compartment or can be located in such annular compartment.
The guide can constitute a converted blank which has been treated in a noncutting shaping machine, e.g., in a press, in a deep drawing machine or the like.
The end portion of the guide is or can be adjacent the support for the housing and can include a flange which extends at least substantially radially of and away from the predetermined axis and can be affixed to the centering portion of the housing.
The guide includes a main portion which is surrounded by the plenum chamber and by the piston; the diameter of the radially outermost part of the end portion of the guide can exceed, and even greatly exceed, the outer diameter of the main portion of the guide. The ratio of the outer diameter of the main portion to the diameter of the radially outermost part of the end portion of the guide can be between 1 and 1.2.
As already mentioned above, the end portion of the guide can include at least one flange which extends at least substantially radially of and away from the predetermined axis; an end face of the housing cooperating with such guide can be provided with a recess for the at least one flange of the guide. The guide can further include a cylindrical extension which is or which can be of one piece with the radially outermost portion of the at least one flange and extends axially and away from the plenum chamber. The centering portion of the housing can include an annular or tubular envelope which surrounds the cylindrical extension; this enhances the centering action of the housing and reduces the likelihood of undesirable tilting of the guide relative to the centering portion of the housing.
The aforementioned second annular flange of the end portion of the guide (i.e., the annular flange which is located radially outwardly of the annular compartment) can abut an at least substantially radially extending surface of the housing; such surface can be in sealing engagement with the second annular flange of the end portion of the guide.
The centering portion of the housing can at least partially fill the annular compartment.
The arrangement is or can be such that the end portion of the guide is centered by the centering portion of the housing at the internal surface of the housing and/or by two discrete portions of the housing one of which can include or constitute the centering portion.
The sealing element which operates between the centering portion of the housing and the end portion of the guide can be installed in a recess provided therefor in an end face of the housing.
Alternatively, and if the centering portion extends into the aforementioned annular compartment defined by the end portion of the guide and the housing, an internal surface of such centering portion can be provided with an annular recess which is located in the annular compartment and receives the sealing element.
Still further, it is possible to install the sealing element in an annular recess provided therefor in the external surface of the end portion of the guide; the centering portion of the housing preferably surrounds such recess and sealingly engages the sealing element.
It is also possible to install the sealing element in an internal recess of centering portion of the housing; such housing and the guide can be provided with cooperating means for locating the guide in a preselected axial position relative to the housing, i.e., relative to the centering portion and the sealing element in the internal recess of the centering portion. The locating means can comprise an internal shoulder provided in the housing and extending radially outwardly from the predetermined axis, and such locating means further comprises an external projection provided at the end portion of the guide adjacent the internal shoulder.
If the sealing element is received in an external surface of the end portion of the guide, the centering portion of the housing preferably surrounds the recess and sealingly engages the sealing element. Such apparatus can further comprise at least substantially annular retaining means anchored in the external surface of the end portion of the guide and cooperating with the centering portion to prevent the sealing element from leaving the recess.
The housing can comprise means for maintaining the guide in a predetermined (optimum) axial position relative to the internal surface; such means can be designed to operate by snap action. The end portion of the guide can be provided with a tubular extension, and the means for maintaining the guide in a predetermined axial position relative to the internal surface of the housing can include at least one prong, arm, tooth or a like part provided at the centering portion of the housing and engaging the extension.
The centering portion of the housing can be provided with a surface which confronts the adjacent axial end of the plenum chamber and is formed with an annular recess for the end portion of the guide.
The end portion of the guide can be a press fit in the centering portion of the housing. For example, the external surface of the guide can include a smaller-diameter portion which is surrounded by the piston, and a larger-diameter portion which is a press fit in the centering portion of the housing. The larger-diameter portion of the external surface of the guide can have a diameter which is approximately three times the length of the centering portion of the housing.
The end portion of the guide and the centering portion of the housing can define a bayonet mount which serves to hold the housing and the guide against movement relative to each other, particularly against movement longitudinally and circumferentially of the predetermined axis.
The internal surface of the housing, and more particularly that portion of such internal surface which is defined by the centering portion, can be provided with an annular recess for the sealing element; the latter surrounds the adjacent portion of external surface of the guide and the guide can include an annular flange which extends radially outwardly beyond the external surface of the guide and abuts the sealing element. The centering portion of the housing can be provided with a deformed portion which overlies the flange and is utilized to hold the guide against axial movement relative to the housing.
The guide can be caulked to the housing. It is also possible to bond the end portion of the guide to the centering portion. Furthermore, a portion of the external surface or the entire external surface of the guide can be anodized; the anodized portion of such external surface can abut that portion of the internal surface of the housing which is provided on the centering portion.
Still further, it is possible to provide a film of plastic material on that portion of external surface of the guide which abuts the internal surface of the housing.
That (second) end portion of the guide which is remote from the centering portion of the housing can include a radially inwardly extending part which is form-lockingly and/or otherwise engaged by a stop serving to limit the extent of axial movement of the piston in a direction away from the centering portion of the housing. For example, the stop can engage the aforementioned part at the second end portion of the guide by snap action.
The internal surface of the housing and the external surface of the guide can define a relatively narrow annular clearance which is sealed by the sealing element and is adjacent the centering portion of the housing. The guide and/or the housing can be provided with one or more annular corrugations which extend from one of the annular surfaces to the other surface adjacent the sealing element. The corrugation or corrugations can force-lockingly engage the guide and/or the housing.
In accordance with a highly advantageous feature of the present invention, the housing can comprise a hollow cylindrical inner wall which surrounds the shaft and is surrounded by the guide. The guide can sealingly engage the wall at one end and the apparatus can further comprise means for preventing axial movements of the guide relative to the wall; such preventing means can be disposed at the other end of the guide.
At least a portion of the housing can consist of a suitable plastic material.
Furthermore, at least a portion of the guide can consist of a metallic material, such as steel or aluminum.
The novel features which are considered as characteristic of the invention are set forth in particular in the appended claims. The improved clutch actuating apparatus itself, however, both as to its constuction and the modes of assembling, installing and operating the same, together with numerous additional important and advantageous features and attributes thereof, will be best understood upon perusal of the following detailed description of certain presently preferred specific embodiments with reference to the accompanying drawings.